Deconstructing insight: EEG correlates of insightful problem solving.

Abstract

BACKGROUND:

Cognitive insight phenomenon lies at the core of numerous discoveries. Behavioral research indicates four salient features of insightful problem solving: (i) mental impasse, followed by (ii) restructuring of the problem representation, which leads to (iii) a deeper understanding of the problem, and finally culminates in (iv) an "Aha!" feeling of suddenness and obviousness of the solution. However, until now no efforts have been made to investigate the neural mechanisms of these constituent features of insight in a unified framework.

METHODOLOGY/PRINCIPAL FINDINGS:

In an electroencephalographic study using verbal remote associate problems, we identified neural correlates of these four features of insightful problem solving. Hints were provided for unsolved problems or after mental impasse. Subjective ratings of the restructuring process and the feeling of suddenness were obtained on trial-by-trial basis. A negative correlation was found between these two ratings indicating that sudden insightful solutions, where restructuring is a key feature, involve automatic, subconscious recombination of information. Electroencephalogram signals were analyzed in the space x time x frequency domain with a nonparametric cluster randomization test. First, we found strong gamma band responses at parieto-occipital regions which we interpreted as (i) an adjustment of selective attention (leading to a mental impasse or to a correct solution depending on the gamma band power level) and (ii) encoding and retrieval processes for the emergence of spontaneous new solutions. Secondly, we observed an increased upper alpha band response in right temporal regions (suggesting active suppression of weakly activated solution relevant information) for initially unsuccessful trials that after hint presentation led to a correct solution. Finally, for trials with high restructuring, decreased alpha power (suggesting greater cortical excitation) was observed in right prefrontal area.

CONCLUSIONS/SIGNIFICANCE:

Our results provide a first account of cognitive insight by dissociating its constituent components and potential neural correlates.

Relationship between restructuring of the problem and suddenness of the solution.

(A) Relative frequencies as a function of subjective rating of restructuring and suddenness for correct solutions without hint. The higher the rating of suddenness, the more frequent it was. For restructuring ratings the relative frequency distribution was reverse. The higher the rating of restructuring, the less frequent it was. (B) As in (A), but for correct post-hint solutions. After hint presentation the distributions of relative frequencies changed. The higher the rating of restructuring, the higher were the relative frequencies. The four levels of suddenness rating were equally often chosen. (C) Interaction Plot of reaction time with ratings of suddenness and restructuring. Mean reaction times, expressed in Z-scores on the ordinate, are plotted as a function of subjective rating of restructuring for 4 different levels of suddenness. Dotted line: gradually approached correct solution (rating of suddenness = 0); dash-dotted line: rating = 1; dashed line: rating = 2; solid line: solution appeared abruptly without any conscious forewarning (rating = 3). The interaction plot displays, that the longer the required time for a correct solution was, (i) the higher was the subjective rating of restructuring and (ii) the lower was the suddenness feeling. Thus, the shortest reaction times were found for sudden solutions with no restructuring and the longest reaction times were found for non-sudden solutions with full restructuring. ’.’, ’*’, ’* *’ and ’* * *’ correspond to significance levels p<0.1, p<0.05, p<0.01 and p<0.001 of a Wilcoxon signed rank test, respectively.

Significant clusters of the nonparametric cluster randomization tests for mental impasse and timeout.

(A) Comparison of mental impasse with timeout trials. Top left: topographical map of the parieto-occipital gamma band cluster displaying significant differences between the baseline-corrected spectral power of mental impasse and timeout with P<0.005. Top right: topography of the occipital theta band cluster for the same comparison. Bottom: Pseudo-color coded time-frequency representation in decibel (dB) of the difference between mental impasse and timeout averaged over electrodes PO3, Oz and PO4. Red color indicates higher spectral power for mental impasse and blue color indicates higher spectral power for timeout. Mental impasse response or timeout is at t = 0 s. (B) Comparison of the immediate pre- and post- hint presentation time period after reaching a mental impasse between hints that led to a correct solution versus those that led to a timeout trials. Topographical map on the left shows the right parieto-occipital gamma band cluster, displaying significant (P<0.04) differences. Top right: Pseudo-color coded, grand-averaged time-frequency representation of all electrodes that comprise the significant cluster. Bottom: grand-averaged gamma frequency event-related synchronization (ERS) averaged for both conditions between 38 and 52 Hz and for the same electrodes as in the time-frequency representation. The red rectangle marks the zone of significance (p<0.01). Red color indicates higher spectral power for correct solution trials and blue color indicates higher spectral power for timeout trials. (C) As in (B) but comparing the immediate pre- and post- hint presentation time period of hints after timeout that led to a correct solution versus those that led to a further timeout. The dotted red rectangle marks the zone of significance with p<0.05. The white rectangles with solid and dotted lines in the grand averaged time-frequency representation plots show the time-frequency zones of significance with p<0.01 and p<0.05, respectively.

Significant cluster of the nonparametric cluster randomization test for correct solutions involving full restructuring versus those involving no restructuring of problem.

Left: topographical map of the right prefrontal alpha (8–10 Hz) frequency band cluster displaying significant (P<0.075) differences between the baseline-corrected spectral power of correct solutions with full restructuring versus those with no restructuring. Right: Grand averaged time-frequency representation of the difference between correct solutions with full restructuring and those with no restructuring over all electrodes that comprise the significant cluster. Red color indicates higher spectral power for correct solutions with full restructuring and blue color indicates higher spectral power for correct solutions with no restructuring. Time of solution response is at 0 s marked by dotted red line. The white dotted rectangle marks the time-frequency zone of significance (p<0.05).

(A) Left: topography of the bilateral parieto-occipital gamma frequency band cluster (38–44 Hz, P<0.003) displaying significant differences between the baseline-corrected spectral power of sudden and non-sudden solutions. Right: topographies of the right parieto-occipital gamma band cluster (38–44 Hz, P<0.04) displaying significant differences between the baseline-corrected spectral power of sudden and non-sudden solutions at two different times. (B) Grand averaged time-frequency representation of the difference between sudden and non-sudden solutions for the strongest representant PO4 (in terms of significance), common to both clusters. Red color indicates higher spectral power for sudden solutions and blue color indicates higher spectral power for non-sudden solutions. Time of solution response is at 0 s marked by red dotted vertical line.